7. Project Summary/Abstract Chikungunya virus (CHIKV) is an alphavirus classified as a category C priority pathogen that causes fever, rash, and arthralgia in humans, leading to debilitating illness and a low quality of life. In the past decade, CHIKV outbreaks have spread beyond the endemic regions of Africa and Asia. The World Health Organization reported in 2014 that there were over 1 million suspected cases of Chikungunya in the Caribbean islands and Central and South American countries. While the number of cases has declined since this peak in 2014, the geographic expansion of CHIKV has continued with the most recent outbreak occurring in Pakistan in 2016. Estimates indicate that 1.3 billion people reside in areas at-risk for CHIKV transmission. As a result of this increase in range and number of human cases, CHIKV is considered a re-emerging pathogen; a contributing factor to this re-emergence is the adaptation to transmission by Aedes albopictus mosquitoes. Currently, there are no licensed vaccines or therapeutics to protect against CHIKV infection. As with many emerging viral infections, supportive care is the only available treatment. Given the severe morbidity caused by CHIKV, its swift emergence, and continued expansion, a preventative vaccine is necessary to reduce the disease burden. The leading CHIKV vaccine candidates in development are based on live-attenuated virus, chimeric live- attenuated virus, or virus like particles. These complex compositions introduce the risk of adverse events, as the disease mechanism of clinical CHIKV manifestations are not fully understood. Alternate vaccines utilizing methods that can offer better safety profiles as well as benefits in manufacturing are warranted. We have developed a promising recombinant subunit CHIKV vaccine that induces high levels of neutralizing antibodies and prevents viral replication in immune competent mice. Our data indicate that the conformation of the E2 protein is critical to the ability to induce potent neutralizing antibody responses. This Phase II application expands our initial efforts to develop a CHIKV recombinant subunit vaccine focused on the E2 protein. The proposed research aims to 1) Optimize expression and purification of E2/E1 recombinant protein, 2) Evaluate immunogenicity and protective efficacy of E2/E1 in mouse models, 3) Conduct preliminary vaccine safety study and manufacture master cell bank, and 4) Conduct a pre-IND meeting with the FDA. As with all vaccines, and in particular for priority pathogens such as CHIKV which requires BSL-3 handling, a combination of safety and economics in manufacturing are of paramount importance. The proposed recombinant subunit approach provides a means to deliver a safe, stable, and established manufacturing platform for a CHIKV vaccine.